1. Field of the Invention
The invention relates to a motor unit having a bearing assembly forming a fluid dynamic pressure bearing supported on an inner circumferential portion of a housing member with an adhesive section interposed therein, a manufacturing method and a recording disk driving apparatus.
2. Description of the Related Art
Motor units each having a spindle motor unit equipped with a fluid dynamic pressure bearing in the presence of oil in a micro gap between a shaft and a hollow cylindrical sleeve have been employed in various kinds of electronic equipment such as a recording disk driving apparatus.
In such a motor unit, a sleeve is securely held on an inner circumferential portion of a housing member with an adhesive section interposed therebetween. In the motor unit having such a holding structure, the sleeve is securely held on the housing member by an adhesive force of the adhesive section. Adhesives generally used in this case include: a thermosetting adhesive cured by heating; an ultraviolet curing type adhesive cured by irradiation with ultraviolet, an anaerobic adhesive cured by shutting-off outside air and others.
In a case where the above adhesives are used, the following problems occur, however. A thermosetting adhesive has a high adhesive strength, but it takes a long time to cure the adhesive. Hence, the sleeve and the housing member have to be held in an immobile state with respect to positions thereof using a comparative large scale jig till the applied adhesive cures. Therefore, because it accommodated the motor unit and the jig together in the oven for curing the thermosetting adhesive, the productivity might be not excellent.
An ultraviolet curing adhesive is fast in curing speed, but there arises a case where the ultraviolet curing adhesive is not cured since ultraviolet does not reach a site such as a deep narrow gap.
An anaerobic adhesive is fast in curing speed, but curing is limited to a deep, narrow gap and what's worse, there arises a case where things around or near the adhesive is contaminated by outgassing from the adhesive in an uncured state.